An object is to provide an electron gun that makes it possible to verify whether or not an electron beam emitted form a photocathode is misaligned from a designed emission center axis. The object can be achieved by an electron gun including: a light source; a photocathode; and an anode. The electron gun includes an intermediate electrode arranged between the photocathode and the anode, an electron beam shielding member configured to block a part of an electron beam, a measurement unit configured to measure an intensity of an electron beam blocked by the electron beam shielding member, and an electron beam emission direction deflector arranged between the anode and the electron beam shielding member and configured to change a position where an electron beam that passed through the anode reaches the electron beam shielding member. The intermediate electrode has an electron beam passage hole and a drift space.
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1. An electron gun comprising:
a light source;
a photocathode configured to emit an electron beam in response to receiving light from the light source; and
an anode,
wherein the electron gun includes
an intermediate electrode arranged between the photocathode and the anode,
an electron beam shielding member configured to block a part of an electron beam,
a measurement unit configured to measure an intensity of an electron beam blocked by the electron beam shielding member, and
an electron beam emission direction deflector arranged between the anode and the electron beam shielding member and configured to change a position where an electron beam that passed through the anode reaches the electron beam shielding member, and
wherein the intermediate electrode has
an electron beam passage hole through which an electron beam emitted from the photocathode passes through, and
a drift space is formed in the electron beam passage hole such that, when an electric field is generated between the photocathode and the anode by application of a voltage, effect of the electric field can be disregarded.
8. An emission axis verification method for an electron beam emitted from a photocathode in a device including
a light source,
a photocathode configured to emit an electron beam in response to receiving light from the light source,
an anode,
an intermediate electrode arranged between the photocathode and the anode,
an electron beam shielding member configured to block a part of an electron beam,
a measurement unit configured to measure an intensity of an electron beam blocked by the electron beam shielding member, and
an electron beam emission direction deflector arranged between the anode and the electron beam shielding member and configured to change a position where an electron beam reaches the electron beam shielding member, the emission axis verification method comprising:
a first electron beam emission step of emitting an electron beam in a first state by irradiating the photocathode with excitation light when electric fields between the cathode and the intermediate electrode and between the intermediate electrode and the anode are in a first state;
a first electron beam intensity change measurement step of measuring a change in intensity of a first electron beam blocked by the electron beam shielding member while changing a position of the first electron beam reaching the electron beam shielding member by using the electron beam emission direction deflector;
a second electron beam emission step of emitting an electron beam in a second state by irradiating the photocathode with excitation light when electric fields between the cathode and the intermediate electrode and between the intermediate electrode and the anode are in a second state;
a second electron beam intensity change measurement step of measuring a change in intensity of a second electron beam blocked by the electron beam shielding member while changing a position of the second electron beam reaching the electron beam shielding member by using the electron beam emission direction deflector; and
a misalignment verification step of verifying whether or not an electron beam emitted from the photocathode is misaligned from a designed center axis by comparing a measurement result of the first electron beam intensity change measurement step with a measurement result of the second electron beam intensity change measurement step.
2. The electron gun according to
3. The electron gun according to
4. The electron gun according to
5. The electron gun according to
6. The electron gun according to
7. An electron beam applicator comprising the electron gun according to
a free electron laser accelerator,
an electron microscope,
an electron holography device,
an electron beam drawing device,
an electron diffractometer,
an electron beam inspection device,
an electron beam metal additive manufacturing device,
an electron beam lithography device,
an electron beam processing device,
an electron beam curing device,
an electron beam sterilization device,
an electron beam disinfection device,
a plasma generation device,
an atomic element generation device,
a spin-polarized electron beam generation device,
a cathodoluminescence device, or
an inverse photoemission spectroscopy device.
9. The emission axis verification method according to
the first state of the electric fields between the cathode and the intermediate electrode and between the intermediate electrode and the anode and
the second state of the electric fields between the cathode and the intermediate electrode and between the intermediate electrode and the anode
is performed by a change of a value of voltage applied to the intermediate electrode.
10. The emission axis verification method according to
the first state of the electric fields between the cathode and the intermediate electrode and between the intermediate electrode and the anode and
the second state of the electric fields between the cathode and the intermediate electrode and between the intermediate electrode and the anode
is performed by a change of a position of the intermediate electrode between the cathode and the anode.
11. An emission axis alignment method for an electron beam emitted from a photocathode, the emission axis alignment method comprising:
a light source position adjustment step and/or a photocathode position adjustment step performed after the misalignment verification step of the emission axis verification method according to
12. The electron gun according to
13. The electron gun according to
14. The electron gun according to
15. The electron gun according to
16. The electron gun according to
17. The electron gun according to
18. The electron gun according to
19. The electron gun according to
20. The electron gun according to
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This application is a U.S. National Phase application, under 35 U.S.C. § 371, of International Application no. PCT/JP2020/033515, with an international filing date of Sep. 4, 2020, and claims priority to Japanese application no. 2019-173319, filed on Sep. 24, 2019, each of which is hereby incorporated by reference for all purposes.
The disclosure of the present application relates to an electron gun, an electron beam applicator, an emission axis verification method for an electron beam emitted from a photocathode, and an emission axis alignment method for an electron beam emitted from a photocathode.
Devices such as an electron gun equipped with a photocathode, an electron microscope, a free electron laser accelerator, an inspection device, or the like including the electron gun (hereafter, a device including an electron gun may be simply referred to as a “device”) are known (see Patent Literature 1).
A device having an electron gun is required to obtain a bright image and high resolution. Thus, such a device requires adjusting work for the emission axis of an electron beam emitted from an electron gun so that the electron beam emitted from the electron gun align with the optical axis of the electron optics of the device when the electron gun is initially mounted or when the electron gun is replaced. Further, also during normal operation, correction of axis misalignment of the electron beam is performed, when necessary, in order to correct misalignment between the electron beam emitted from an electron gun and the optical axis of the electron optics of the device caused by a temporal change or the like (hereafter, correction of axis misalignment of an electron beam may be referred to as “alignment”).
While alignment is often operated manually after an electron gun is mounted to a device, many studies for automation of alignment have been made in recent years. As a related art, there is a method of automatically optimizing an incident axis of an electron beam relative to an anode electrode by driving a motor to perform a mechanical scan of an electron gun, adjusting the incident axis of the electron beam relative to an opening of an annular anode electrode, and automatically acquiring the optimal mechanical position of the electron gun when the amount of current passing through the opening of the anode electrode becomes the largest (see Patent Literature 2).
As another related art, there is also a method for a device that includes: an electron gun configured to emit an electron beam; a focusing coil configured to focuses the electron beam; an alignment component configured to cause the electron beam to enter the center of the focusing coil; and an alignment control unit having digital observation optics configured to observe an irradiation image of the electron beam, an image processing unit configured to process image data from the digital observation optics, and a control unit configured to control the electron gun, the focusing coil, and the alignment component based on processing data from the image processing unit. The control unit of the alignment control unit controls the electron gun and the focusing coil, irradiates a target with an electron beam in predetermined states with different focuses, and outputs an alignment control signal to the alignment component based on a correction value calculated from a difference between position coordinates of the irradiation images (see Patent Literature 3).
As electron guns, a thermionic emission type, a field emission type, and a Schottky type are conventionally known. Among these types, the thermionic emission type is superior in the amount of probe current, the stability of current, the price, and the like and are thus widely used in general purpose SEMs, EPMAs, Auger analyzers, and the like. Thus, most studies related to automation of alignment such as disclosure of Patent Literatures 2 and 3 are for thermionic emission type electron guns.
On the other hand, the electron gun equipped with a photocathode disclosed in Patent Literature 1 can emit a bright, sharp electron beam by irradiating the photocathode with excitation light. Thus, such electron guns have been developed in recent years. However, electron guns equipped with a photocathode are under development, and there is no known method to utilize a characteristic of the photocathode to verify whether or not there is misalignment of an electron beam emitted from a photocathode.
The present inventors have newly found through intensive studies that a combination of:
Accordingly, an object of the disclosure of the present application relates to an electron gun that can verify whether or not an electron beam emitted from a photocathode is misaligned from the designed emission center axis, an electron beam applicator equipped with the electron gun, an emission axis verification method for an electron beam emitted from a photocathode, and an emission axis alignment method for an electron beam emitted from a photocathode.
The present application relates to an electron gun, an electron beam applicator, an emission axis verification method for an electron beam emitted from a photocathode, and an emission axis alignment method for an electron beam emitted from a photocathode illustrated below.
According to the disclosure of the present application, it is possible to verify whether or not there is misalignment between the designed emission center axis and the center axis of an electron beam actually emitted from a photocathode.
An electron gun, an electron beam applicator, an emission axis verification method for an electron beam emitted from a photocathode, and an emission axis alignment method for an electron beam emitted from a photocathode will be described below in detail with reference to the drawings. Note that, in the following embodiments, “emission axis verification method for an electron beam emitted from a photocathode” and “emission axis alignment method for an electron beam emitted from a photocathode” are described as “emission axis verification method for an electron gun” and “emission axis alignment method for an electron gun”, respectively. Further, in the present specification, members having the same type of functions are labeled with the same or similar references. Further, duplicated description for the members labeled with the same or similar references may be omitted.
Further, the position, size, range, or the like of respective components illustrated in the drawings may be depicted differently from the actual position, size, range, or the like for easier understanding. Thus, the disclosure in the present application is not necessarily limited to the position, size, range, or the like disclosed in the drawings.
Definition of Direction
In the present specification, a direction in which an electron beam emitted from a photocathode travels toward an anode without being bent on the way is defined as a Z-axis direction. Note that, while the Z-axis direction is the perpendicularly downward direction, for example, the Z-axis direction is not limited to the perpendicularly downward direction. Further, a direction orthogonal to the Z-axis direction is defined as an X-axis direction, and a direction orthogonal to the Z-axis direction and the X-axis direction is defined as a Y-axis direction.
An electron gun 1A in the first embodiment will be described with reference to
The electron gun 1A in the first embodiment includes at least a light source 2, a photocathode 3, an anode 4, the electron beam shielding member 5, a measurement unit 6, an intermediate electrode 7, and an electron beam emission direction deflector (hereafter, also referred to as a “deflector”) 8. Optionally, additionally, the electron gun 1A may include a photocathode housing container 9 that houses the photocathode 3. Further, optionally, additionally, the electron gun 1A may include power supply devices 11a and 11b used for generating an electric field between the photocathode 3 and the intermediate electrode 7 and between the intermediate electrode 7 and the anode 4, respectively.
The light source 2 is not particularly limited as long as it can irradiate the photocathode 3 with excitation light L to cause the electron beam B to be emitted. The light source 2 may be, for example, a high power (watt order) and high frequency (several hundred MHz) ultrashort pulse laser light source, a relatively inexpensive laser diode, an LED, or the like. The emitted excitation light L may be any of pulse light or continuous light and may be controlled as appropriate in accordance with the purpose. Note that, in the example illustrated in
In the example illustrated in
The photocathode 3 is formed of a substrate 31 of quartz glass, sapphire glass, or the like and a photocathode film (not illustrated) adhered to the first surface (the surface on the anode 4 side) of the substrate 31. The photocathode material for forming the photocathode film is not particularly limited as long as it can emit an electron beam when irradiated with excitation light and may be made of a material requiring EA surface treatment, a material not requiring EA surface treatment, or the like. The material requiring EA surface treatment may be, for example, a group III-V semiconductor material or a group II-VI semiconductor material. Specifically, AlN, Ce2Te, GaN, a compound of one or more types of alkali metals and Sb, AlAs, GaP, GaAs, GaSb, InAs, or the like, and a mixed crystal thereof, or the like may be used. Another example may be a metal, specifically, Mg, Cu, Nb, LaB6, SeB6, Ag, or the like. With EA surface treatment being performed on the photocathode material, the photocathode 3 can be fabricated, and for the photocathode 3, not only can excitation light be selected in the near-ultraviolet-infrared wavelength region in accordance with gap energy of a semiconductor but also desired electron beam source performance (quantum yield, durability, monochromaticity, time response, spin polarization) in accordance with a use of the electron beam can be obtained through selection of the material or the structure of the semiconductor.
Further, the material not requiring EA surface treatment may be, for example, a single metal, an alloy or a metal compound of Cu, Mg, Sm, Tb, Y, or the like or diamond, WBaO, Cs2Te, or the like. The photocathode not requiring EA surface treatment can be fabricated by a known method (for example, see Japanese Patent No. 3537779). The contents disclosed in Japanese Patent No. 3537779 are incorporated in this specification by reference in their entirety.
The anode 4 is not particularly limited as long as it can generate an electric field with the cathode 3, and an anode commonly used in the field of electron guns can be used.
The arrangement of the power supply device is not particularly limited as long as the electron beam B can be emitted from the cathode 3 to the anode 4 through the intermediate electrode 7. In the example illustrated in
The electron beam shielding member 5 has a hole 51 through which a part of the electron beam B emitted from the photocathode 3 passes.
In the first embodiment, the width of the hole 51 is smaller than the width of the electron beam B. As illustrated in
Alternatively, the width of the electron beam B may be smaller than the hole 51. The electron gun 1 disclosed in the present application uses the deflector 8 to deflect the emission direction of an electron beam. Therefore, even when the width of the electron beam B is smaller than the hole 51, a measurement electron beam blocked by the electron beam shielding member 5 can be obtained. The sizes of D1 and D2 can be suitably set taking into consideration of not only the use for verifying the emission axis of the electron gun 1A but also the operation efficiency of the electron gun 1A or the like.
The material of the electron beam shielding member 5 is not particularly limited as long as it is a conductor or a semiconductor. For example, in the case of a conductor, a metal such as stainless steel (SUS), copper, or the like may be used.
The measurement unit 6 measures the intensity of the measurement electron beam that is a part of the electron beam B blocked by the electron beam shielding member 5. The measurement unit 6 is not particularly limited as long as it can measure the intensity of the measurement electron beam. For example, when the electron beam shielding member 5 is a conductor, current occurs between the electron beam shielding member 5 and the measurement unit 6 due to the measurement electron beam. Thus, the intensity of the electron beam B can be measured as a value of current by the measurement unit 6. Note that the value of current can be measured by using a known ammeter though depiction thereof is omitted. Further, a measured value of current depends on the amount of the electron beam B blocked by the electron beam shielding member 5. Further, the value of current occurring when the measurement electron beam hits the semiconductor can be measured by using a semiconductor as the electron beam shielding member 5.
The measurement unit 6 may measure the intensity of the measurement electron beam by fluorescent intensity instead of a value of current. More specifically, a conductor on which a fluorescent material has been applied in advance may be used as the electron beam shielding member 5, and the fluorescent intensity of light emitted when the measurement electron beam hits the fluorescent material may be measured by the measurement unit 6. Note that a fluorescent intensity can be measured by using a known fluorometer.
The intermediate electrode 7 has an electron beam passage hole through which the electron beam B emitted from the photocathode 3 passes, and in the electron beam passage hole, a drift space is formed where effect of an electric field can be disregarded when the electric field is generated between the photocathode 3 and the anode 4 by application of a voltage. The material used for fabricating the intermediate electrode 7 is not particularly limited as long as it is a conductor and may be a metal such as stainless steel (SUS) or the like. Note that the structure of the intermediate electrode 7 is well known as disclosed in Japanese Patent No. 6466020. In Japanese Patent No. 6466020, however, the intermediate electrode 7 is used for adjusting a focal distance of the electron beam B. In contrast, in the electron gun 1A according to the first embodiment, the purpose of use of the intermediate electrode 7 differs in that, when used in combination with the electron beam shielding member 5, the measurement unit 6, and the deflector 8, the intermediate electrode 7 can also be used for verifying as to whether or not the electron beam B emitted from the photocathode 3 is misaligned from the designed emission center axis, as described later. Obviously, the intermediate electrode 7 may be used for adjustment of the focal distance of the electron beam B along with the verification of misalignment of the electron beam B. The content disclosed in Japanese Patent No. 6466020 is incorporated in the present specification by reference in its entirety.
The deflector 8 is not particularly limited as long as it can change, in the X-axis direction and the Y-axis direction, the position where the electron beam B that has passed through the anode 4 reaches the electron beam shielding member 5. Examples of the deflector 8 may be a magnetic field type deflection coil in which two pairs of coils orthogonal to each other are formed as a set and the axis alignment can be made by two-dimensional deflection, an electrostatic type beam deflector, or the like. Note that, as the deflector, the electrostatic type is the more preferable, because influence of noise is smaller and the device is simpler.
An overview of the first embodiment of an emission axis verification method for an electron gun (hereafter, also simply referred to as a “verification method”) will be described with reference to
First, the reason why a verification method according to the first embodiment is necessary will be described with reference to
The electron gun 1A emits an electron beam when a portion irradiated with the excitation light L from the light source 2 of the photocathode (photocathode film) 3 is excited. In assembly of the electron gun 1A, a designed irradiation position 3c of the photocathode 3 to be irradiated with the excitation light L is determined so that an electron beam emitted from the photocathode 3 is emitted in the Z-axis direction toward the center of the anode 4. The light source 2 is then positioned so that the excitation light L from the light source 2 is emitted to the designed irradiation position 3c of the photocathode 3. As illustrated in
In contrast, as illustrated in
Next, each step of the first embodiment of the verification method will be described with reference to
In the first step (ST1), a first electron beam emission step is performed. In the first electron beam emission step (ST1), as illustrated in
In the second step (ST2), a first electron beam intensity change measurement step is performed. In the first electron beam intensity change measurement step (ST2), the intensity of a measurement electron beam blocked by the electron beam shielding member 5 of the first electron beam B1 is measured by the measurement unit 6. In this process, the position of the first electron beam B1 reaching the electron beam shielding member 5 is changed in the X-axis direction and the Y-axis direction by the deflector 8 illustrated in
In the third step (ST3), a second electron beam emission step is performed. The second electron beam emission step (ST3) is the same as the first electron beam emission step (ST1) except for being performed in a second state of the electric fields between the cathode 3 and the intermediate electrode 7 and between the intermediate electrode 7 and the anode 4 generated in the first electron beam emission step (ST1). Thus, duplicated description will be omitted. Note that, in the present specification, an electron beam when emitted in the second state of electric fields between the cathode 3 and the intermediate electrode 7 and between the intermediate electrode 7 and the anode 4 is defined as a “second electron beam B2”.
In the fourth step (ST4), a second electron beam intensity change measurement step (ST4) is performed. The second electron beam intensity change measurement step (ST4) is the same as the first electron beam intensity change measurement step (ST2) except that the electron beam reaching the electron beam shielding member 5 is the second electron beam B2. Thus, duplicated description will be omitted.
In the fifth step (ST5), a misalignment verification step (ST5) is performed. In the misalignment verification step (ST5), it is verified whether or not the electron beam emitted from the photocathode 3 is misaligned from the designed emission center axis Bc by comparing the measurement result of the first electron beam intensity change measurement step (ST2) with the measurement result of the second electron beam intensity change measurement step (ST4).
The principle that makes it possible to verify whether or not the electron beam B emitted from the photocathode 3 is misaligned from the designed emission center axis Bc in accordance with the first embodiment of the verification method will be described with reference to
Overview of Intermediate Electrode 7
First, the overview of the intermediate electrode 7 will be described with reference to
The range that the generated electric field EF strongly affects the movement of an electron beam in a gap is inside a sphere including a circle as the maximum cross section when the opening of the gap is the circle. In other words, when the diameter of the electron beam input port 72 illustrated in
As described above, when D/(a/2+b/2) is larger than 1, a drift space 74 is formed. The value D/(a/2+b/2) is not particularly limited as long as it is larger than 1. However, to increase the range of misalignment between the center axes of the first electron beam B1 and the second electron beam B2 when reaching the electron beam shielding member 5, it is preferable that the drift space 74 have some extent of length, and the value may be suitably set to 1.5 or larger, 2 or larger, 3 or larger, 4 or larger, 5 or larger, or the like, for example. On the other hand, as long as the electron beam emitted from the photocathode 3 is within a range that can pass through the electron beam passage hole 71, there is no particular upper limit for D/(a/2+b/2). However, when D/(a/2+b/2) is larger, in other words, when the length D of the electron beam passage hole 71 is excessively longer, there is a problem of an increase in size of the electron gun 1A. Therefore, D/(a/2+b/2) is preferably 1000 or less in terms of device design, and can be suitably set to 500 or less, 100 or less, 50 or less, or the like, when necessary.
Note that, although the intermediate electrode 7 has a hollow cylindrical shape and the electron beam passage hole 71 is cone-shaped in the example illustrated in
While the intermediate electrode 7 can be arranged anywhere between the cathode 3 and the anode 4, when the arrangement position of the intermediate electrode 7 is excessively close to the cathode 3 or the anode 4, in other words, exceeds the discharge limit, no electron beam will be released. Therefore, the intermediate electrode 7 can be arranged so that the distance between the cathode 3 and the anode 4 does not exceeds the discharge limit.
Further, although the intermediate electrode 7 is formed as a single member in the example illustrated in
Next, movement of an electron (electron beam) when the intermediate electrode 7 having the drift space 74 is provided between the cathode 3 and the anode 4 will be described with reference to
It is known that, when passing through an electric field (EF), an electron beam (electron) is subjected to force from the electric field based on the following principle.
More specifically, as illustrated in
On the other hand,
Next, differences between the first electron beam emission step and the second electron beam emission step will be described with reference to
On the other hand, since the potential difference between the cathode 3 and the anode 4 is constant, the potential difference between the intermediate electrode 7 and the anode 4 will change opposite to the potential difference between the cathode 3 and the intermediate electrode 7. That is, since the potential difference between the intermediate electrode 7 and the anode 4 is larger in
In contrast, a case where the first electron beam emission step and the second electron beam emission step are performed in the state illustrated in
Next, the first electron beam intensity change measurement step (ST2), the second electron beam intensity change measurement step (ST4), and the misalignment verification step (ST5) will be described with reference to
First,
Next, the overview of the second electron beam intensity change measurement step (ST4) will be described with reference to
As illustrated in
Note that, in
Next, the overview of the first electron beam intensity change measurement step (ST2) when the positional relationship of the members that make up the electron gun 1A is not correct will be described with reference to
Next, the overview of the second electron beam intensity change measurement step (ST4) when the positional relationship of the members that make up the electron gun 1A is not correct will be described with reference to
As described above, in the first electron beam intensity change measurement step (ST2) and the second electron beam intensity change measurement step (ST4), the measured value of current and the voltage applied to the deflector 8 are plotted in a graph or the like to find a correlation between the value of current measured by the measurement unit and the voltage applied to the deflector 8. Then, in the first electron beam intensity change measurement step (ST2) and the second electron beam intensity change measurement step (ST4), while the voltages of the deflector 8 resulting in the left-right symmetrical graph are the same when the positional relationship of the members that make up the electron gun 1A is correct, the values of voltage of the deflector 8 resulting in the left-right symmetrical graph are different from each other when the positional relationship of the members that make up the electron gun 1A is not correct. Therefore, in the misalignment verification step (ST5), by comparing the measurement results of the first electron beam intensity change measurement step (ST2) and the second electron beam intensity change measurement step (ST4) with each other, it is possible to confirm that the positional relationship of the members that make up the electron gun 1A is correct when the voltages of the deflector 8 where the graph is left-right symmetrical are the same, and it is possible to confirm that the positional relationship of the members that make up the electron gun 1A is misaligned from the correct state when the values of voltage are different.
Note that, for easier understanding, the above description has been provided assuming that, when the positional relationship of the members that make up the electron gun 1A is correct, the voltages of the deflector 8 resulting in left-right symmetrical graph are the same (0). Alternatively, the values of voltage of the deflector 8 resulting in left-right symmetrical graphs measured in the first electron beam intensity change measurement step (ST2) and the second electron beam intensity change measurement step (ST4) may not be 0 in a strict sense and may be different from each other as long as these values of voltage are within design tolerance. The degree of misalignment considered within the tolerance can be suitably adjusted in a design process.
Further, although
An increased voltage applied to the deflector 8 results in a larger amount of deflection of the first electron beam B1 and the second electron beam B2. Therefore, the inclination from the designed emission center axis Bc of the first electron beam B1 and the second electron beam B2 when reaching the electron beam shielding member 5, namely, the irradiation angle relative to the electron beam shielding member 5 more deviates from the perpendicular direction as the voltage applied to the deflector 8 increases. Thus, the irradiation conditions of the first electron beam B1 and the second electron beam B2 when reaching the electron beam shielding member 5 will change in accordance with the voltage applied to the deflector 8.
Since the electron gun 1A is assembled while the positional relationship of the component members is being verified, the electron beam B emitted from the photocathode 3 is not significantly misaligned from the designed emission center axis Bc. Thus, even when one set of the deflector 8 is used to deflect the first electron beam B1 and the second electron beam B2, the verification method according to the first embodiment can be performed, because the irradiation conditions of the first electron beam B1 and the second electron beam B2 when reaching the electron beam shielding member 5 do not significantly change.
On the other hand, when two sets of the deflector 8a and the deflector 8b are used, the first electron beam B1 and the second electron beam B2 can be emitted to the electron beam shielding member 5 from substantially the perpendicular direction. In other words, regardless of the voltage applied to the deflector 8, the irradiation conditions of the first electron beam B1 and the second electron beam B2 when reaching the electron beam shielding member 5 can be the same. Therefore, the use of two sets of the deflector 8a and the deflector 8b can further increase the accuracy of the verification method.
In the first embodiment of the electron gun 1A and the first embodiment of the emission axis verification method for the electron gun (hereafter, also simply referred to as “the first embodiment”), the first state and the second state are implemented by changing the voltage applied to the intermediate electrode 7 with respect to the electric fields between the cathode 3 and the intermediate electrode 7 and between the intermediate electrode 7 and the anode 4. A modified example of the first embodiment (hereafter, also simply referred to as “the modified example”) differs from the first embodiment in that the first state and the second state are changed by employing a drive unit (method) that moves the position of the intermediate electrode 7 arranged between the photocathode 3 and the anode 4 in the designed emission center axis direction of an electron beam, and other features are the same. Accordingly, in the modified example, features different from the first embodiment will be mainly described, and duplicated description for the features that have already been described in the first embodiment will be omitted. It is thus apparent that, even when not explicitly described in the modified example, the feature that has already been described in the first embodiment can be employed in the modified example.
The modified example will be more specifically described with reference to
In the example illustrated in
On the other hand, the density of equipotential lines between the intermediate electrode 7 and the anode 4 is opposite to that between the cathode 3 and the intermediate electrode 7. That is, the density of equipotential lines between the intermediate electrode 7 and the anode 4 is larger in the order from
As described above, also in the modified example, the first state and the second state can be adjusted with respect to the electric fields between the cathode 3 and the intermediate electrode 7 and between the intermediate electrode 7 and the anode 4.
The electron gun 1A and the verification method according to the first embodiment and the modified example achieve an advantageous effect that it is possible to verify whether or not there is misalignment of the designed emission center axis due to a temporal change of a member that make up the electron gun 1A, mechanical shock, or the like.
A second embodiment of the electron gun 1 will be described with reference to
As described above, with the first embodiment and the modified example, it is possible to verify whether or not the electron beam B emitted from the electron gun 1A is misaligned from the designed emission center axis Bc. Therefore, the first embodiment and the modified example can be used for an emission axis alignment method performed at the initial setting when the electron gun 1 is mounted to the counterpart device E.
As illustrated in
The electron gun 1B according to the second embodiment includes the light source position adjustment member 21. Thus, the light source position adjustment member 21 is driven based on the above calculation, and thereby the excitation light L emitted from the light source 2 can be adjusted to irradiate the designed irradiation position 3c of the photocathode 3.
The light source position adjustment member 21 is not particularly limited as long as it can adjust excitation light emitted from the light source 2 in the X-axis direction and the Y-axis direction. For example, the light source 2 can be attached to a known XY-axis stage, and the position of the light source 2 can be changed. Alternatively, although depiction is omitted, a reflection mirror may be arranged between the light source 2 and the photocathode 3 to deflect the emission direction of the excitation light L. Note that, although the excitation light L from the light source 2 is arranged at a position to irradiate the first face of the photocathode 3 in the example illustrated in
The electron gun 1B according to the second embodiment can be used in an emission axis alignment method for the electron gun (hereafter, also referred to as “axis alignment method”).
The third embodiment of the electron gun 1 will be described with reference to
The photocathode kit 3a includes at least the photocathode 3 (photocathode film), a lens 32 for focusing the focal point on the photocathode film, and a holder 33 and is held by the holder 33 so that the distance between the photocathode 3 and the lens 32 is unchanged. In an example illustrated in
In the example illustrated in
The photocathode position adjustment member 35 needs to adjust the position of the photocathode kit 3a, which is arranged inside the vacuum chamber CB (vacuum region), from outside of the vacuum chamber CB (vacuum region). It is thus desirable for the photocathode position adjustment member 35 to include an extra-chamber power transmission member 35a arranged outside the vacuum chamber CB (vacuum region) and an intra-chamber power transmission member 35b arranged inside the vacuum chamber CB (vacuum region). In the example illustrated in
International Publication No. 2018/186294 discloses an example in which the intra-chamber power transmission member 35b mainly performs driving in the Z-axis direction. However, when the size of the hole at a position where the intra-chamber power transmission member 35b is inserted in the vacuum chamber CB is set to be larger than the intra-chamber power transmission member 35b, it is possible to move the intra-chamber power transmission member 35b in the X-axis direction and the Y-axis direction in addition to the Z-axis direction. As a result, the position of the photocathode 3 can be adjusted in both the X-axis direction and the Y-axis direction. The extra-chamber power transmission member 35a is not particularly limited as long as it can drive the hole-less wall 35d in the X-axis direction, the Y-axis direction, and the Z-axis direction, and a known XYZ stage may be used. Note that the example described above illustrates an example of the photocathode position adjustment member 35. The photocathode position adjustment member 35 is not limited to the above example as long as it can adjust the position of the photocathode 3 from outside of the vacuum chamber CB (vacuum region).
When the electron gun 1C according to the third embodiment is used, the light source position adjustment member 21 can be adjusted in accordance with the amount of misalignment from the designed emission center axis. Note that, unlike the electron gun 1A according to the first embodiment, the electron gun 1C according to the third embodiment is provided with the lens 32 such that the focal point is focused on the photocathode film. Thus, with adjustment of only the light source position adjustment member 21, the excitation light L may be unable to irradiate the designed irradiation position 3c. In such a case, adjustment can be performed together with the photocathode position adjustment member 35. Alternatively, it is also assumed that, although the position of the light source 2 is correct, the installation position of the photocathode kit 3a may be misaligned. In such a case, only the photocathode position adjustment member 35 may be used to adjust the position of the photocathode 3.
In the second embodiment of the emission axis alignment method for the electron gun, the light source position adjustment step (ST6) of the first embodiment of the emission axis alignment method for the electron gun can be replaced with a light source position adjustment step and/or a photocathode position adjustment step (ST6).
The fourth embodiment of the electron gun 1 will be described with reference to
The level of misalignment between the designed emission center axis for an electron beam and the electron beam B emitted from the photocathode 3 can be calculated manually. In the electron gun 1D according to the fourth embodiment, however, whether or not there is misalignment and the amount of misalignment are calculated by the calculation unit 13 based on the measurement value measured by the measurement unit 6. Further, the electron gun 1D includes the control unit 14 that drives and controls the light source position adjustment member 21 in accordance with the calculation result calculated by the calculation unit 13. Therefore, the use of the electron gun 1D according to the fourth embodiment achieves an advantageous effect that the misalignment verification step (ST5) and the light source position adjustment step (ST6) can be automated. Note that it is apparent that the electron gun 1D according to the fourth embodiment is applicable to the electron gun 1C according to the third embodiment. In such a case, the control unit 14 drives and controls the light source position adjustment member 21 and/or the photocathode position adjustment member 35.
The fifth embodiment of the electron gun 1 will be described with reference to
According to the electron gun 1 of the second to fourth embodiments described above, the electron gun 1 can emit the electron beam B along the designed emission center axis Bc. After the electron gun 1 is mounted to the counterpart device E, however, misalignment may be found between the designed emission center axis Bc and the incident axis BE of the counterpart device E. In such a case, the amount of the electron beam B set by the counterpart device E will not be provided for incidence. Since the electron gun 1E according to the fifth embodiment includes the electron beam deflector 81 that deflects the electron beam B that has passed through the electron beam shielding member 5, it is possible to align the incident axis BE of the counterpart device E to which the electron gun 1E is mounted with the emission direction of the electron beam B emitted from the electron gun 1E.
Whether or not there is misalignment between the incident axis BE of the counterpart device E and the emission direction of the electron beam B emitted from the electron gun 1E can be detected in accordance with whether or not a predetermined amount of electron beam reaches an electron beam intensity detector such as a Faraday cup provided to the counterpart device E or the like. Further, a known device that can deflect an electron beam can be used for the electron beam deflector 81, and, for example, a device similar to the electron beam emission direction deflector 8 can be used. Note that, in the example illustrated in
The electron beam applicator E to which an electron gun is mounted may be a known device to which an electron gun is mounted. The electron beam applicator E may be, for example, a free electron laser accelerator, an electron microscope, an electron holography device, an electron beam drawing device, an electron diffractometer, an electron beam inspection device, an electron beam metal additive manufacturing device, an electron beam lithography device, an electron beam processing device, an electron beam curing device, an electron beam sterilization device, an electron beam disinfection device, a plasma generation device, an atomic element generation device, a spin-polarized electron beam generation device, a cathodoluminescence device, an inverse photoemission spectroscopy device, or the like.
Note that, in the above embodiments of the verification method and the axis alignment method, all of the intermediate electrode 7, the electron beam shielding member 5, the measurement unit 6, and the deflector 8 are arranged in the electron gun 1, and thereby the embodiments have been described as the verification method and the axis alignment method for the electron gun 1. Alternatively, all of the members except for the intermediate electrode 7 or some of these members may not be provided to the electron gun 1. More specifically, all the members or some member(s) of the electron beam shielding member 5, the measurement unit 6, and the deflector 8 may be provided to the counterpart device E. Further, all the members or some member(s) of the electron beam shielding member 5, the measurement unit 6, and the deflector 8 may be provided as a kit separate from the electron gun 1 and the counterpart device E.
As described in the above embodiments of the verification method and the axis alignment method, the combined use of the intermediate electrode 7, the electron beam shielding member 5, the measurement unit 6, and the deflector 8 makes it possible to verify whether or not the electron beam B emitted from the photocathode 3 is misaligned from the designed emission center axis Bc. Therefore, when some or all of the electron beam shielding member 5, the measurement unit 6, and the deflector 8 are arranged in a part other than the electron gun 1, “emission axis verification method for an electron gun” and “emission axis alignment method for an electron gun” can be replaced with “emission axis verification method for an electron beam emitted from a photocathode” and “emission axis alignment method for an electron beam emitted from a photocathode”, respectively.
The use of the electron gun, the electron beam applicator, the emission axis verification method for an electron beam emitted from a photocathode, and the emission axis alignment method for an electron beam emitted from a photocathode disclosed in the present application makes it possible to verify whether or not an electron beam is emitted along a designed emission center axis. Therefore, the electron gun, the electron beam applicator, the method of verifying an emission axis of an electron beam emitted from a photocathode, and the method of aligning an emission axis of an electron beam emitted from a photocathode disclosed in the present application are useful for business entities that handle an electron beam emitted from a photocathode of an electron gun or the like.
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